In Wyoming, as in many of the Rocky Mountain states, there has been but very little detailed geological work done, and our present very limited knowledge is largely based on the reports of the early reconnaissance surveys. Large areas remain unknown to science that have not been mapped or approximately described. These are more common than is generally supposed, and often contain several hundred square miles. One of these areas extends from the Union Pacific railroad, in Carbon county, north to the Laramie mountains, and from the North Platte river eastward more than 50 miles, and includes the great dinosaur fields that have recently attracted considerable attention, and also constitutes an important portion of the territory to be considered in this paper.
In southeastern Wyoming, or that portion of the state lying east of the South Platte river and south of the Fremont, Elkhorn and Missouri Valley railroad, the . . .